KUEAL EISTGINEEEING. 777 



A method of correcting river discharge for a changing stage, B. E. Jones 

 (U. S. Oeol. Survey, Wafer-Supphj Paper 375-E {1915), pp. 111-130, figs. 6).— 

 It is pointed out in tliis paper that " wlien a river is rising fast it has a greater 

 velocity and a greater discharge than it has at the same height when its stage 

 is constant. Liljewise, when it is falling fast it has a lesser velocity and a 

 lesser discharge. For this reason the relation of gage height to discharge 

 which applies under conditions of constant stage will not apply during times of 

 changing stage, . . . especially ... if the slope of the river is small. . . . The 

 increased discharge at a given gage height during a rising stage is due to the 

 increase in slope, and the opposite is true for a falling stage. Therefore, the 

 smaller the natural slope of the stream the greater is the proportional change in 

 slope for any given rate of change in the stage." 



For the purpose of correcting the discharge for a changing stage so that 

 proper relations between gage height and discharge may be established for 

 certain conditions the following formula, based on Chezy's formula for flow of 

 water in open channels, is mathematically derived : 



N 



/i V 



In this formula Oi=the discharge at constant stage, Q2=the discharge for 

 changing stage, /Si— slope at constant stage, iL=rate of change of stage per sec- 

 ond, y=tlie mean velocity of the measurement made during the changing stage, 

 and iV=the coefficient " for obtaining mean velocity from surface velocitj\" It 

 is assumed that the flood travels very nearly at the rate of the surface velocity. 

 " Therefore, to obtain the velocity of the flood, that is, the surface velocity — the 

 mean velocity of the measurement should be divided by 0.9 for large streams and 

 by 0.85 for smaller ones. ... In order to compute the actual discharge from 

 gage heights observed during a changing stage it is necessary to have the 

 cross section at the gage and a slope curve in addition to the discharge curve 

 and mean velocity curve for constant stage. Then the discharge may be as- 

 sumed to be equal to that at the same gage height at a constant stage, and 

 the approximate mean velocity, surface velocity, and corrected discharge may 

 be obtained. The corrected discharge may then be used in obtaining a new 

 surface velocity and a second correction obtained. This can be repeated until 

 the error is negligible, but once will usually be sufficient." 



Data from actual applications of this method are also given. 



Conditions requiring the use of automatic gages in obtaining records of 

 stream flow, C H. Piekce (L^ S. Geol. Survey, Water-Supphj Paper 315-F 

 (1915), pp. 131-139, figs. 6). — The conditions which require the use of auto- 

 matic gages are summarized as follows: (1) Regulation of the stream by power 

 developments, (2) operation of canals and ditches delivering water for irriga- 

 tion, (3) fluctuations due to variation in run-off under natural conditions (a) 

 caused by rain and (6) caused by melting ice and snow, (4) inaccessibility of 

 gaging station or lack of reliable observer, (5) continuous record needed for 

 legal purposes, and (6) human fallibility of most gage observers. These condi- 

 tions a.re briefly discussed. 



Small automobile opens up new opportunities in Government stream gag- 

 ing work, E. A. PoBTEB (Engin. Rec, 71 {1915), No. 16, pp. PO, Jf91, figs. 3).— 

 Data collected by the U. S. Geological Survey indicate that in a number of the 

 Western States the small automobile is more efficient in stream measurement 

 worli than a team. 



